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Show 6() DROSERA ROTUNDIFOLIA. CIL·\P. IV. CHAPTER IV. THE EFFECTS OF HEAT ON TilE LEAVES. Nature of the experiments- Effects of boiling water-Warm water causes rapid inflection- Water at a high?r temperature uo s not · cause immediate inflection, but does not lnll tho loav s, as Hhown by their subsequent re-expansion and by tho. aggroga.tion of tho protoplasm-A still higher temperature k1lls tho loaves ancl coagulates the albuminous contents of the glands. IN my observations on Drosera rotundifolia, tho I avos seemed to be more quickly infl cted over animal substances, and to remain inflect d for a 1 ng r perio<l during very warm than during cold weather. I wished, therefore, to ascertain wh ther h at alone would induce inflection, and what tern perature was the most efficient. Another interesting point presented itself, namely, at what degree lif was extinguished; for Drosera offers unusual faciliti s in this respect, not in the loss of the pow r of infl( ction, but in that of subsequent re-expansion, and more especially in the failure of the protoplasm to become aggregated, when the leaves after being heated are immersed in a solution of carbonate of an1monia.*· *When my experiments on tho effects of heat were u1ade, I was not aware that the subject had been carefully investigated by several observers. For instance, Sachs is convinced (' 'rmite do Botanique,' 1874, pp. 772, 854 ) that the most different kinds of plants all perish if kept for ld m. in water at 45° to 40° Cent., or 113° to 115° Fahr.; and he con-elude that tho protopla~m within their cells alway::; con.gulato. , if in a clamp condition, at a temperature of between 50° n.nd 60° Cont., or 12:!.0 to 140° Fahr. Max Schultze and Kii.hno (a::; quoted by Dr. lltt, tian in 'Coutomp. Hoviow,' 187-:1:, p. 52 ) "found that tho protoplasm or plantcollR, with which th 'Y xp rimented, was always kill <1 and CHAP. IV. THE EFFECTS OF HEAT. 67 :My experiments were tried in the following manner. Loaves were cut off, and this does not in the least interfere with their powers; for instance, three cut-off leaves, with bits of meat placed on them, were kept in a damp atmosphere, and after 23 hrs. closely embraced the meat both with their tentacles and blades; and the protoplasm within their cells was well aggregated. Three ounces of doubly distilled water was heated in a porcelain vessel, with a delicate thermometer having a long bulb obliquely suspended in it. The water was gradually raised to the required temperature by a spirit-lamp moved about under the vessel; and in all cases the leaves were continually waved for some minutes close to the bulb. They were then placed in cold water, or in a solution of carbonate of ammonia. In other cases they were left in the water, which had been raised to a certain temperature, until it cooled. Again in other cases the leaves were suddenly plunged into water of a certain temperature, and kept there for a t:;pecified time. Considering that the tentacles are extremely delicate, and that their coats are very thin, it seems scarcely possible that the fluid contents of their cells should not have been heated to within a degree or two of the temperature of the surrounding water. Any further precautions would, I think, have been superfluous, as the leaves from age or constitutional causes differ slightly in their sensitiveness to heat. It will be convenient first briefly to describe the effects of immersion for thirty seconds in boiling water. The leaves arc rendered flaccid, with their tentacles bowed backwards, which, as we shall see in a future chapter, is probably due to their outer surfaces retaining their elasticity for a longer period than their inner surfaces retain the power of contraction. The purple fluid within the cells of the pedicels is rendered finely granular, but there is no true aggregation; nor does this follow altered by a very brief exposure to a temperature of l18~0 Fahr. as a maximum." As my results are deduced from special phenomena, namely, tho subsequent aggregation of tho protoplasm and the re-oxpansion of the tentacles, they seem to me worth giving. We shall find that Drosera resists heat somewhat better than most other plantR. That there should be consider-able differences in this mspect is not surprising, considering that some low vegetable orga.nisms grow in hot springs - cases of which have been collected by Prof. Wyman(' American Journal of Science,' vol. xliv. 1867). Thus, Dr. Hooker found Oonfervro in water at 168° Fa.ln·.; Humboldt, at 185° Fahr.; and DeseloizemlX, at 208° Fahr. F 2 |